Commutator and the like



8. R. BERGMAN- COMMUTATOB AND THE LIKE- APPLICATION FILED SEPT. a. 1920.

lllllmml I Inventor: 5ven R .Berrgman,

b5 vt/fiw/ mm H is Attorneg.

Patented June 13, 1922,

PATENT OFF-ICE.

SVEN n. BERGMAN,

OF NAHAN T, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

GO'MMUIATOR. AND THE LIKE.

Specification ofLetters Patent.

Patented. June 13, 1922.

Application filed September 3, 1920. Serial No; 407,829.

T 0 all whom it may concern Be it known that I, Sven R. BERGMAN, a subject of the Kin of Sweden, residing at Nahant, county'ot lnssex, State of Massachusetts, have invented certain new and useful Improvements in Commutators and the like, of which the following is a specification.

The present invention relates to commutators or similar devices for dynamo electricv machines which devices comprise ring shaped members which are required to be clamped to and; insulated from the rotating shaft or other rotating part of the machine. The object of my invention is to provide an. improved insulating and clamping or holdingmeans for such ring members which is particularly well adapted for use in high voltage, or high speed machines or both, although due to its simplicity and low manufacturing cost it may be advantageously applied to any machine. I have :lound my invention-to be oi particularly great utility in connection with the commutators'of high voltage or high speed, or both highvoltage and high speed direct current machines for by use of it I am enabled to use higher voltages and speeds in direct current machines than have heretofore been considered feasible. I have accordingly specifically illustrated and clescribed this use of my invention in the present application.

Prior to my invention, great difliculty has been encountered in the construction of commutators for high voltage or high speed machines, the commutatorsbeing the primary limiting elements in such machines. In standard practice the ring of commutator segments or bars is held between wedgeshaped mica cones, and to obtain cones of sui'iicient thickness to withstand high voltage without creepage to ground it is necessary to build up such mica cones from sheets oi mica stuck together by a suitable adhesive material such as shellac. This forms what is known as pasted mica and since it has poor insulating qualities as compared with pure mica a greater thickness is required for the same dielectric strength. However, the limit in thickness of pasted mica cones is soon reached on account of the mechanical difficulties in maintaining the cones in place against centrifugal force and in keeping them from becoming loose due to centrifugal force and heating, the heating causing distortion of the parts between which the cones are hold. A mica cone possesses no resiliency and when the commutator bars expand and contract .due to heat, the metallic holders distort with the result that the commutator bars become loose.

In this connection, it is customary to provide a nut for tightening the clamping means for the ring of commutator segments but even with frequent adjustments this has not made it possible to hold the ring satisfactorily in the case of large cones such as are required for high voltage or in the case of high speed, machines. It has also been proposed'to use a yielding metallic spring means for holding the clamping members always in engagement with the ring of commutator segments but such an arrangement is open to objectionv that the metallic spring soon takes a permanent set and ceases to function and also to the objection that it is very ditlicult in the first instance to obtain a metallic yielding spring oi correct strength, andeven if of correctstrengthin the first instance it will not remainso.

As a result the. voltage and speed for commutator machines ihas-Qnecessarily remained comparativelylowldue to the diiiiculty of constructing a satisfactory commutator for high voltage, high speed, or both. i

By my invention, 1 overcome the above referred to difiicult-ies and am enabled to build commutatorsfor voltages and speeds of very high value without danger of creep age to ground, the breaking down electrically of the insulation, or mechanical trouble.

For a consideration of what'I believe to be novel and my invention, attention is directed to the accompanying description and the claims appended thereto.

In the drawing, Fig. 1 is a side elevation partly in section of a commutator embodying my invention; and Fig. 2 is a similar view of another embodiment, the arrangement of Fig. 2 being more particularly intended for much higher voltages than that of Fig. 1.

Referring to both figures of the drawing,

5 indicates commutator segments or bars separated by insulating segments 6 in the usual manner, the segments when assembled forming a ring.

Now, according to my invention, I clamp the ring of commutator segments between metallic end members between which and the ends of the bars is mounted resilient insulating material which is capable of withstanding the working temperatures met with and which can be highly compressed with out destroying its resilient properties. Such a material is found in spinnable textile fibres and it is this substance which I now prefer to use in carrying out my invention. Preferably I mount the ring of commutator segments on a sleeve or tube of insulating material, which sleeve or tube is in turn mounted on a tubular holder, and I clamp the resilient insulating material under compression in engagement with said ring of segments by means of end members carried by the tubular holder. By thus clamping the ring of commutator segments between resilient insulating means, such insulating means will yield sufiiciently to permit of the expansion of the commutator segments axially thereby avoiding stresses such as would distort the metallic holders; and when the commutator segments contract again, the resilient insulating means will follow the movement. As a result, the ring of commutator segments will always be held firmly and will not become loose.

Referring now specifically to Fig. 1 wherein is illustrated a commutator which while not adapted for high voltages is well adapted for high speeds, the ring of commutator segments is mounted on an insulating tube 7 supported either directly or indirectly on a holder 8. In the present instance, tube 7 is shown as being supported at its two ends by insulating rings 9 arranged between the tube and holder 8. Tube 7 and rings 9 may be made advantageously of layers of paper rolled up and stuck together with shellac, bakelite or the like, this being a known structure of insulating tube and one having high dielectric strength. The ring of commutator segments is clamped between metallic end members 10 and 11 between which and the ends of the segments are interposed resilient insulating rings 12. Rings 12 are clamped under high compression by end members 10 and 11, the pressure not being sufiicient, however, to break down the fibres of the material in case the rings comprise spinnable textile fibres. In the present instance, the end member 10 is shown as being formed integral with holder 8 while the end member 11 is a separate piece fixed in place on the other end of holder 8. For this purpose the end of holder 8 projects throu h member 11 and is expanded against it. The end members 10 and 11 are undercut and the ends of conducting segments 5 and insulating segments 6 slope outwardly so as to provide a firm anchoring of both the ring of commutator segments and the insulating rings between the end members.

In constructing a commutator as shown in Fig. 1, I first provide the rings 12 in the form of flat washers made from a resilient insulating material. In case spinnable textile fibres are used in making the rings, I preferably take cotton batting, soak it in water to soften it and then compress it into sheets, the compression being of the order of 12,000 lbs. per square inch, so as to squeeze the greater portion of the water out, and form a fiat sheet. The soaking may be done in a vacuum tank and a small amount of suitable substance, such as starch may be added to the water, to form a temporary binder to assist in handling the batting. From the sheets thus formed suitable rings or washers 12 are cut by suitable dies. These rings or washers are then baked in an oven for a suiiicient period to remove the moisture from them. I then take a holder 8 having the flange 10 at one end, the other end being straight, mount the parts thereon in the order shown, and then subject the structure to heavy end pressure to compress the insulating rings between the ring of commutator segments and the end members 10 and 11. When sufiiciently compressed, I expand the end of holder 8 against the outer surface of end member 11 as shown to hold the parts in position. In compressing the parts together I may use, in the case of spinnable textile fibres, a pressure of the order of 8,000 to 10,000 pounds per square inch.

Preferably the rings or washers 12 are as sembled on the holder and compressed while hot to guard against the presence of any moisture.

The commutator as thus formed is then machined to dimensions after which it is preferably again baked at a suitable tenr perature and given a number of coats of moisture-proof insulating material such as varnish, each coat being baked dry. The material penetrates the resilient insulating material a certain amount thereby making it moisture-proof. It is desirable that this moisture-proof insulating material be elastic when dry so that it will not crack due to expansion and contraction of the commutator and any suitable moisture-proof insulating material possessing this property may be used. F or example, I have found what is known as Sterling varnish satisfactory.

In constructing a commutator for high voltages, I use in connection with the resilient insulating material other insulating material such as mica or bakelite, which, while not resilient is a better insulator so as to increase both the dielectric strength and the creepage to ground distance. In such structures I preferably use alternate layers of the resilient material and the non-resilient insulation, the same taking the form of flat rings or washers. Such a structure is shown in Fig. 2 wherein the ring of commutator segments is mounted on a shellacked paper'tube 7 a of the same character as tube 7 shown in Fig. 1. Tube 7 is mounted on a holdereS. The ring of commutator segments is held between metallic end members 10 and 11 betweenwhich and the ring are in terposed alternate rings or washers of resilient material 12 and non-resilient insulating material 1 1. End member 10 is shown as being formed integral with holder 8 while endmember 11 is formed separately therefrom and is heldin place by a nut 15 which screws onto the end of holder 8 arrangement I have shown the tube 7 as being of substantially the length of holder 8 terminating short of nut 15 by an amount just sufficient to prevent interfering with tightening up nut 15. The insulatingmembers 12 and 14 slip over tube ,7 as does end member 11. This gives a very simple structure which can be manufactured at a low cost. In this connection it will be noted that the main part of the structure for holding the commutator segments is built up of tubes and flat rings which are in substance washers and can be produced: in quantities very cheaply, and assembled without special machinery. I

The arrangement of Fig. 2 is constructed after the manner described in connection with Fig. 1 and is set up under a pressure of substantially the same order. Likewise the end members 10 and 11 are undercut and the ends of the bars 5 and insulating segments 6 slope outwardly so as to firmly anchor the parts. With this arrangement the insulating members 12 and 14 take the shape of dished washers. The sloping ends of the ring of commutator segments may be provided with circumferential grooves as shown at 16 into which material of the adj acent resilient insulating rings 12 is pressed to more firmly anchor the commutator ring.

Since in a commutator built in accordance with my invention, the ring of commutator segments is held in place by a resilient insulating material exerting heavy pressure on the ends of the segments, the segments cannot come loose, the arrangement thus insuring a tight commutator. Furthermore, no means for tightening the holding or clamping members is necessary or need be provided since the commutator segments cannot come loose even under the most severe operating conditions. hen the commutator segments become heated and expand, the resilient material by which they are held will In this material, since if put under suflicient pressure to crush the fibres, they lose their resiliency to a. greater or less extent.

My improved commutator also possesses the substantial advantage that there is a large saving in the material required for the commutator bars over that heretofore required since the bars are of little depth. This is an important item from a cost stand point since such bars are in general made of copper. There isal'so a saving in cost of material since spinnable textile fibre material such as cotton batting, for example, is cheaper than insulating materials such as mica, for example; and there is a further saving in manufacturing cost because of the few and simple parts of which the commutator may be constructed. I i

In accordance with the provisions ofthe patent statutes, I have described the principle of operation of my invention together with the apparatus which I now consider to represent the best embodiment thereof, but I desire to have it understood that the apparatus shown is only illustrative and the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination, aJrotary ring member for conveying electric current, clamping means therefor, and resilient insulating means interposed between said ring member and clamping means and held under compression by said clamping means.

2. In combination, a rotary ring member for conveying electric :current, clamping means therefor comprising a holder which extends through the ring and clamping end members on the holder, and resilient insulating means located between the ring member and the end members and held under compression by said end members.

3. In combination, a rotary ring member for conveying electric current, clamping means therefor, and resilient insulating means comprising spinnable textile fibrous material interposed between said ring memher and clamping means and held under con'ipression by said clamping means.

4. In combination, a rotary ring member for conveying electric current, an insulating tube 011 which it is mounted, end clamping members, and resilient insulating material interposed between the ends of said ring and said end clamping members and held finder compression by said clamping memere.

5. In combination, a current conducting posed between said clamping means and said ring, said insulating means comprising layers of resilient insulating material and nonresilient insulating material.

6. In combination, a current conducting rotary ring member, clamping means therefor, resilient insulating means interposed between said clamping means and said ring, said insulating means comprising layers of spinnable textile fibrous material and nonresilient insulating material.

7. In combination, an insulating tube, a currentconducting rotary ring member mounted. thereon, resilient insulating material engaging the ends of said ring member, and clamping means holding said material under compression against the ends of said ring member to maintain it in position thereon.

8. In combination, an insulating tube, acurrentconducting rotary ring member mounted thereon, resilient insulating means comprising alternate layers of resilient ma.- terial and non-resilient insulating material engaging the ends of said ring member, and. end clamping means for holding said resilient insulating means under compression.

9. A commutator comprising a ring of alternate conducting and non-conducting segments, clamping means for the ends ot the ring, and insulating means interposed. between said clamping means and the ring, characterized by the fact that said insulating means comprises resilient insulatingmaterial held under compression by said clamping means.

10. A commutator comprising a ring oi alternate conducting and non conducting segments, clamping means for the ends of the ring, and insulating means interposed between said clamping means and the rin characterized by the fact that said insulating means comprises spinnable textile fibrous material held under compression by said clamping means.

11. A commutator comprising a ring of alternate conducting and non-conducting segments, clamping means for the ends of the ring, and insulating means interposed between said clamping means and the ring, characterized by the fact that said insulating means comprises alternate layers of re silient material and non-resilient insulating material held under compression by said clamping means.

12. A commutator comprising an insulating tube, a ring of alternate conducting and non-conducting segments mounted thereon, resilient insulating means mounted on said tube in engagement with the ends of said ring, and clamping means holding said insulating means under compression.

13. A rotary ring for conducting electric current, means for holding it comprising spinnable textile lib-res, and clamping means which holds: said fibers under compression of a substantial order.

14. In combination, a tubular support having an integral flange at one end, a tube of insulating material carried by the support, a ring for conducting electric current mounted on said tube, resilient insulating means located between said ring and flange, a flange at the other end of said support, and resilient insulating means located be tween the ring and said last named flange, said insulating means being clamped between said ring and flanges under heavy pressure.

In witness whereof, I have hereunto set my hand this 31st day of August, 1920.

SVEN R. BERGMAN. 

